11 January 2014

Following up on a December 2013 over-the-air software upgrade to the Model S to enable safer charging under certain conditions, Tesla Motors announced that it has also designed an improved wall adapter with a thermal fuse. Tesla will provide this upgraded adapter to existing and new customers free of charge starting in a few weeks. Both measures are designed to reduce the risk of garage fires.

In its release, Tesla noted that a variety of factors such as corrosion, physical damage to receptacles, or inappropriate wiring or installation of electrical outlets can cause higher than normal electrical resistance when using the Universal Mobile Connector (UMC) NEMA 14-50 adapters to charge Tesla Model S vehicles. When charging, higher than normal electrical resistance connections to external energy sources may cause excessive heating of the adapter. This, in extreme cases, could result in melting or a fire.

The December over-the-air software update addresses this issue, enabling the Model S onboard charging system automatically to reduce the charging current by 25% if it detects unexpected fluctuations in the input power to the vehicle.

This fully addresses the issue by substantially reducing the heat generated in any high resistance connections outside the vehicle, Tesla said. This update increases robustness and safety considerably in the unlikely event that a home wiring system, receptacle, adapter or cord is unable to meet its rated current capacity.

Because this was an over-the-air update, customers can confirm receipt without having to bring their vehicles into a Tesla Service Center or other location by simply tapping on the 17" touchscreen and verifying that their Model S is running software version 5.8.4 or later. Any vehicle that is not within range of the wireless network or is not remotely accessible for any other reason can have the update installed through Tesla authorized Service Centers or Tesla Rangers.

However, to provide another layer of assurance to Model S customers using the 14-50 socket, Tesla designed the improved wall adapter with a thermal fuse. Even if the circuit breakers on the house side and car side don’t trip, the thermal fuse will prevent current from flowing if the wall socket region heats up for any reason. Tesla said that although it does not believe the improved adapter is required to address the issue, it is taking this step as part of its commitment to full customer satisfaction.

Tesla has also informed the National Highway Traffic Safety Administration of these proactive measures.

Tesla had one of these in the first Roadster portable charge cables (not sure if they used the same mechanism or not as they'll be using on the Model S UMC).

They got rid of it because it tended to generate false trips if the plug sat in the sun while charging.

Definitely agree that one really should be using a hard-wired charging station at home.

Still - thermosensors just seem like a good idea at these connectors - even on the J1772 plug. There have been multiple cases of J1772 plugs melting to the car due to out-of-spec plugs.

Put a $0.50 thermistor in the car and dial down the charge rate as appropriate should the temperature in the receptacle reach a critical temp. Then do the same thing in the plug/adapter for your portable charge plug.

Not rocket science and should be very inexpensive compared to the bad press a fire generates.